The fluid pump can be a lubricant pump, a coolant pump, a vacuum pump, or a pump providing pressurized liquid or gas, for example, pressurized air. The mechanical fluid pump is not driven by an electric motor, but is directly connected to the combustion engine. The rotational speed of the fluid pump is therefore proportional to the rotational speed of the combustion engine so that the fluid pump always rotates even if no need exists for a fluid supply or for a suction activity to create a vacuum.
U.S. Pat. No. 7,422,093 B2 describes a fluid pump for providing a pressurized liquid for a hydraulic power steering. The fluid pump is provided with a magneto-rheological clutch so that the pump performance can be controlled depending on the fluid demand and pressure demand of the power steering.
A risk of failure is not acceptable for vital fluid pumps, such as a lubricant pump, a coolant pump, or a vacuum pump for a pneumatic brake assistance unit. The fluid pump including the clutch should be as compact as possible. A relatively high torque must be coupled by the clutch in many applications.